The present invention relates to an electromagnetic flow meter that can be inserted and clamped between two flanges of piping conveying a fluid that is to be measured. More particularly, the present invention pertains to a structure for such an electromagnetic flow meter.
In constructing a conventional electromagnetic flow meter, a measuring pipe made of a non-magnetic metal is inserted through an opening in the axial end face of an outer casing made of a magnetic metal, and the end portions of the measuring pipe are secured to the outer casing by means of welding. Electrode bosses are inserted through an opening in the outer casing in a direction perpendicular to the axis of the measuring pipe and are welded to the measuring pipe. Insulating spacers then are threaded into the electrode bosses, and an insulating lining is provided on the inner surface of the measuring pipe. Then, electrodes are inserted into the insulating spacers from the inner surface of the measuring pipe and are secured. Thereafter, a pair of magnet cores provided with exciting coils are mounted by inserting them from the open ends of upper and lower magnetic flux generating unit housing portions, which are formed on the outer casing so as to extend orthogonally to the axis of the measuring pipe and to the electrodes.
After assembly, the only way possible to confirm whether or not the structural symmetry required for the electromagnetic flow meter has satisfactorily been obtained is by visually checking the outside of the apparatus. The apparatus, however, is housed in the outer casing, and it is therefore difficult to effect any accurate confirmation. For this reason, it is necessary to increase substantially the degree of machining accuracy to ensure the required symmetry and reduce the distance between the upper and lower magnetic flux generating units, which fact inevitably increases the costs. Moreover, it is difficult to conduct such assembling operations as mounting the constituent elements and handling the lead wires extending from the electrodes and the magnetic flux generating units, which must be carried out in the narrow space within the outer casing. It is therefore not easy to reduce the time required for assembly.
One example of a prior art electromagnetic flow meter that can be inserted and clamped between two flanges of piping conveying fluid to be measured is disclosed in U.S. Pat. No. 4,253,340. In this example, a splittable outer casing and the magnet cores are integral with each other, and coils are mounted on the cores. Accordingly, although the outer casing comprises two splittable portions, and these portions are bonded together during assembly, it is still difficult to confirm the structural symmetry of the flow meter and reduce the distance between the upper and lower magnetic flux generating units, because the magnet cores are applied at the same time as the outer casing, which prevents the assembler from checking the accuracy of the assembly.
An electromagnetic flow meter representing earlier work of the present inventor is disclosed in Japanese Patent Disclosure (Kokai) No. 61-151429. In this example, the splittable outer casing and the magnetic cores are not in contact with each other. Therefore, it is difficult to set the outer casing in proper position in relation to the magnetic cores, the electrodes and the measuring pipe. Since the outer casing position affects the magnetic field in the measuring pipe, it is desired that the outer casing position is easily adjustable and easily confirmed in relation to the measuring pipe. In addition, if the outer casing is made of magnetic metal, and if the magnetic cores are in contact with the outer casing, the intensity of the magnetic field in the measuring pipe increases, which is preferable.